Intermittent misfire
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Intermittent misfire
Hi guys, first post here, so please bear with me if I've missed something. Hoping to get some input on what could be going on... I have a 99 4runner 6 cylinder with 140K. Been trying to correct an intermittent problem for the past couple months. Sometimes the engine starts to run rough and the CEL starts to flash for a short time, but never stays on. These two things happen for a few miles and then it starts to run again just fine. I've changed the spark plugs and wires (both NGK), MAF sensor, and the time belt & water pump were replaced about 20K miles ago. It used to be weeks between these occurrences, so each time i changed something I thought i fixed it. Now it's happening more often. I bought a OBD II reader for $40 bucks and at first it said i had no codes. I finally got some codes today while it was acting up- P0300 P0301 P0302 (all had a pending status- not sure what that means, just something the reader showed). So with the cylinders 1 and 2 acting up, it doesn't look like it's a coil. Thinking it may be fuel injectors or perhaps the fuel filter?? Any thoughts. Just thought I give it another try before bringing it to the shop. Suggestions?
#2
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Check the crank bolt torque:
http://www.motor.com/MAGAZINE/Articles/012007_04.html
Quote from link above:
http://www.motor.com/MAGAZINE/Articles/012007_04.html
Quote from link above:
If the crank bolt loosens up, it allows the harmonic balancer and crank sprocket to shake back and forth. First, this unwanted movement usually causes an rpm-sensitive noise and vibration in the front of the engine. You can watch the harmonic balancer wobbling while the engine is idling. Beyond a point, those drive belts are the only things keeping the balancer on the crank snout. It's anyone's guess as to how long a driver will ignore this noise and vibration.
Second, although the loose crank sprocket causes an erratic CKP signal, experience shows that it rarely triggers a crank sensor trouble code. However, the unstable signal creates an assortment of driveability problems. For instance, the engine often idles okay but misfires during acceleration and the ECM sets one or more misfire codes. Eventually, the engine may misfire all the time and become hard to start. Before you dive into a diagnosis, always get the vehicle history and watch for a wobbling harmonic balancer.
When in doubt, thoroughly test the crank sensor with your oscilloscope. Look for the familiar, cyclical, sine wave-like pattern at idle and higher rpm. (Note that a flat spot among the reluctor teeth creates a crisp, repeatable pattern “blip” representing piston position.) Sprocket movement causes an ugly, erratic crank sensor pattern.
A driver may ignore the noise, vibration and misfiring symptoms until it's way too late. By that point, the loose parts may allow the woodruff key to wear or wallow out the keyways in the crankshaft and/or crank sprocket! The unwanted movement also may distort the woodruff key itself. Sometimes the wear and looseness allows the crank sprocket to twist or shift far enough to alter timing; then overall performance suffers. So if you discover a wobbling harmonic balancer and a loose crank bolt on one of these Toyota engines, a tear-down and thorough visual inspection is the best way to know what's damaged and how badly.
Second, although the loose crank sprocket causes an erratic CKP signal, experience shows that it rarely triggers a crank sensor trouble code. However, the unstable signal creates an assortment of driveability problems. For instance, the engine often idles okay but misfires during acceleration and the ECM sets one or more misfire codes. Eventually, the engine may misfire all the time and become hard to start. Before you dive into a diagnosis, always get the vehicle history and watch for a wobbling harmonic balancer.
When in doubt, thoroughly test the crank sensor with your oscilloscope. Look for the familiar, cyclical, sine wave-like pattern at idle and higher rpm. (Note that a flat spot among the reluctor teeth creates a crisp, repeatable pattern “blip” representing piston position.) Sprocket movement causes an ugly, erratic crank sensor pattern.
A driver may ignore the noise, vibration and misfiring symptoms until it's way too late. By that point, the loose parts may allow the woodruff key to wear or wallow out the keyways in the crankshaft and/or crank sprocket! The unwanted movement also may distort the woodruff key itself. Sometimes the wear and looseness allows the crank sprocket to twist or shift far enough to alter timing; then overall performance suffers. So if you discover a wobbling harmonic balancer and a loose crank bolt on one of these Toyota engines, a tear-down and thorough visual inspection is the best way to know what's damaged and how badly.
Last edited by mt_goat; 03-10-2009 at 10:00 AM.
#3
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Here's a big thread about that problem: https://www.yotatech.com/forums/f2/c...ighway-128206/
#4
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I found my problem by jumping to teminals T1 and E1 in the diag plug under the hood. I think those are the ones I used, but this lets you read the base timing. Jump the terminals and put a timing light on it. The timing on mine was jumping around. I tore it down and found that the crank gear was worn out in the keyway. Good luck.
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